1. Field of Invention
The invention relates to a unit and a program for displaying a map, the unit including a first memory for storing map data and a drawing memory for drawing the map data and displaying display-area data of a drawing area in the drawing memory on a display while editing the map in accordance with selected edit information.
2. Description of Related Art
In navigation systems, a map scroll operation is performed on a screen to display a simulation route from the current location to a destination on a map screen in sequence, to track-display the current location with the actual traveling, and to set a starting point, a destination, and a detour on the map.
For example, there have been proposed navigation systems in which, when a map is scrolled with the current location and a route displayed thereon, a determination frame is placed inside a display area and the scrolling is controlled depending on whether a target point is present, thereby eliminating useless scroll operations (JP Publication No. 2000-275050, paras [0011], [0055] and [0056], FIGS. 4–6).
Various data and various data constructions are used to display a map in navigation systems. One of the data used for map display is satellite photograph data. Because the satellite photograph data is large in size, it is generally compressed (by Joint Photographic Experts Group method: JPEG, etc.) when stored in a map disc (storage medium). The compressed data must be decompressed before such satellite photograph data is displayed.
The process for decompressing JPEG compressed data with high compressibility takes a lot of time, thus posing the problem of too low follow-up capability to catch up the display when the current location is tracked and scrolled using the satellite photograph data displayed by a car navigation system.
Various propositions have been put forth (JP Publications Nos. 5-018767, paras [0022]–[0026], FIG. 6 and 2000-283784, para [0025]) regarding map displays in the car navigation systems, one of which is a system of displaying a route guide map on a display screen such that the luminosity of the display screen and a color palette is changed with time so as to prevent the display from becoming hard to view with a change in day-to-night ambient luminosity. However, it takes a lot of processing time to change colors using the color palette, thus having the problem of taking a long time particularly when the number of colors to be changed is large.
Another proposition has described a system in which two kinds of satellite photograph data for daytime and nighttime are stored in a storage medium and data is switched from daytime satellite photograph data to nighttime satellite photograph data in synchronization with a car lighting switch. The system, however, has the problem of requiring a storage medium for storing two pieces of satellite photograph data on the same location thereby increasing the cost of the entire system.